Techniques for reducing and/or eliminating secondary modes in a dye laser oscillator

Abstract

A dye laser master oscillator is disclosed herein. This oscillator is intended to provide a single mode output, that is, a primary beam of light of a specific wavelength, but also has the tendency to provide secondary modes, that is, secondary beams of light at different wavelengths and slightly off-axis with respect to the primary beam as a result of grazing incident reflections within the dye cell forming part of the master oscillator. Also disclosed herein are a number of different techniques for reducing or eliminating these secondary modes.

What is claimed is: 
     
       1. In a dye laser oscillator which is designed to produce at its output a primary light beam at one specific wavelength and along a specific primary axis by passing a continuous stream of dye through a dye cell and simultaneously directing a pump beam through a window in the dye cell to intercept the continuous stream of dye, but which also produces at the oscillator's output a secondary light beam at a different wavelength and slightly off-axis with respect to said primary axis as a result of grazing incidence reflections off the inner axially extending surfaces within the dye cell forming part of the master oscillator, the improvement comprising means entirely within said dye cell acting on said reflected secondary beam for reducing the number of grazing incidence reflections, thereby reducing the intensity of said reflected secondary beam without reducing or substantially reducing the intensity of said primary light beam. 
     
     
       2. The improvement according to claim 1 wherein said secondary beam intensity reducing means includes an anti-reflection coating on said inner axially extending surfaces of said dye cell for absorbing at least some of the light of said secondary beam. 
     
     
       3. The improvement according to claim 2 wherein said inner surfaces include a surface defining a window through which a pump beam is intended to pass for pumping the dye within said dye cell. 
     
     
       4. The improvement according to claim 1 wherein said secondary beam intensity reducing means includes the combination of said dye and said inner axially extending surfaces which are selected to have at least substantially equal indices of refraction, whereby to reduce the amount of light from the secondary beam reflected off of said inner surfaces. 
     
     
       5. The improvement according to claim 4 wherein said inner surfaces includes a surface which forms one surface of a window through which a pump beam is intended to pass for pumping the dye within said dye cell and wherein the difference in said indexes of refractions is at most 10 -4 . 
     
     
       6. In a dye laser master oscillator for producing a primary light beam along a specific primary axis and including a dye cell through which a continuous stream of dye is caused to pass, means for directing a pump beam into said dye cell through a cooperating window in the dye cell and parallel to said specific primary axis for pumping the dye therein, and means including a beam expander, an etalon, a grating and an end mirror located outside of the dye cell on said primary axis, said grating and said end mirror located on opposite sides of the dye cell, and cooperating with the dye cell and the pumped dye passing therethrough for producing at the output of the oscillator said primary light beam along said specific primary axis, the improvement comprising an anti-reflection coating on the inner wall of said dye cell forming part of said cooperating wndow and therefore parallel to said primary axis for absorbing at least a portion of any light which is reflected off of said inner wall. 
     
     
       7. In a dye laser master oscillator for producing a primary light beam along a specific primary axis and including a dye cell through which a continuous stream of dye is caused to pass, means for directing a pump beam into said dye cell through a cooperating window in the dye cell and parallel to said specific primary axis for pumping the dye therein, and means including a beam expander, an etalon, a grating and an end mirror located outside of the dye cell on said primary axis, said grating and said end mirror located on opposite sides of the dye cell and cooperating with the dye cell and the pumped dye passing therethrough for producing at the output of the oscillator said primary light beam at one specific wavelength and along said specific primary axis, the improvement comprising the utilization of said dye and the material forming said cooperating window through which said pumping passes into the dye cell such that said dye and window material have substantially equal indexes of refraction whereby to minimize the possibility of light reflecting off the inner surface of said window within said dye cell. 
     
     
       8. In a dye laser master oscillator for producing a primary light beam along a specific primary axis and including a dye cell through which a continuous stream of dye is caused to pass, means for directing a pump beam into said dye cell through a cooperating window thereof for pumping the dye therein, and means including a beam expander, an etalon, a grating and an end mirror located outside of said dye cell on said primary axis, said grating and said end mirror located on opposite sides of the dye cell and cooperating with the dye cell and the pumped dye passing therethrough for producing at the output of the oscillator said primary light beam at one specific wavelength and along said specific primary axis, the improvement comprising providing said cooperating window into said dye cell at a location perpendicular to said primary axis and providing said pump beam so that it enters said dye cell through said cooperating window along said primary axis so as to provide a pumping zone which is spaced from the inner walls of the dye cell extending parallel to said primary axis, whereby to prevent taking of said dye from taking place at said inner walls. 
     
     
       9. In a method of operating a dye laser master oscillator which is designed to produce at its output a primary light beam at one specific wavelength and along a specific primary axis by passing a continuous stream of dye through a dye cell and simultaneously directing a pump beam through a window in the dye cell to intercept the continuous stream of dye, but which also produces at the oscillator's output a secondary light beam at a different wavelength and slightly off-axis with respect to said primary axis as a result of grazing incidence reflections off an inner axially extending wall within a dye cell forming part of the master oscillator, the improvement comprising the step of acting on said reflected secondary beam entirely within said dye cell for reducing the number of grazing incidence reflections, thereby reducing the intensity of said reflected secondary beam at the output of said oscillator without reducing or substantially reducing the intensity of said primary light beam. 
     
     
       10. The improvement according to claim 9 wherein said step of acting on said secondary beam for reducing its intensity at the output of the oscillator includes the step of coating said inner axially extending wall with a layer of anti-reflection material for absorbing at least some of the light of said secondary beam. 
     
     
       11. The improvement according to claim 9 wherein said step of acting on said secondary beam for reducing its intensity at the output of the oscillator includes the step of selecting said dye and said inner axially extending wall to have at least substantially equal indexes of refraction so as to reduce the amount of light from the secondary beam reflected off of said inner wall. 
     
     
       12. In a dye laser oscillator which is designed to produce at its output a primary light beam at one specific wavelength and along a specific primary axis by passing a continuous stream of dye through a dye cell and simultaneously directing a pump beam through a window in the dye cell to intercept the continuous stream of dye, but which also produces at the oscillator's output a secondary light beam at a different wavelength and slightly off-axis with respect to said primary axis as a result of grazing incidence reflections off the inner axially extending surfaces within a dye cell forming part of the master oscillator, the improvement comprising means entirely within said dye cell and acting on said reflected secondary beam for reducing the number of grazing incidence reflections, thereby reducing the intensity of said reflected secondary beam at the output of said oscillator without reducing or substantially reducing the intensity of said primary light beam, said oscillator including an output coupling mirror outside said dye cell and said secondary beam intensity reducing means including said mirror which is positioned within the path of said secondary beam such that a substantial portion of said secondary beam reflecting off of said coupling mirror is reflected laterally away from and to one side of said dye cell and therefore is not allowed to return to the dye cell for amplification therein.